The D7000 is awesome because it has the best autofocus of any camera for the price, and is the only 'traditional' SLR in that price range from 'the big three' that is fully weather-sealed, and is at least somewhat metal. It is also better at high ISOs than any other camera in that price range, although other models are very close. I wouldn't say that these features make it the 'best' camera at it's price point, but it does make it far and away the most reliable.

When I got my D7000, I had a problem with my Nikon 70-200 VR - it just wasn't sharp. It turns out all my cheaper lenses were fine, and that lens was fine on a friend's D7000. But apparently the way that particular lens was built just didn't jive with that particular camera; it's all sorted out now.

As far as using manual mode ... you don't need to. There are a LOT of people that think using 'more advanced' modes mean that they are using their camera 'better', and that makes them better photographers. This is not true, but if it makes them feel better about themselves I'm not going to try to take it from them. As a photographer of 20+ years, and now a photography professor, I use my camera almost entirely in Aperture mode, with very heavy use of the +
- exposure dial. The fact is that the camera is much smarter than I'll ever be, so why reinvent the wheel?

You should know how your various settings work. You should know for instance that your 18-200 is the sharpest at around f/8-f/16. But the reason you should know this isn't because you need to do the math yourself - it's so that you can understand what the camera is doing if it picks the wrong setting.